a) Career Mode Tournaments : You will have default tournaments in Game Modes / Tournaments. In case you would like to start a Career select this one.
b) Game Mode Tournaments ( No Career Mode) : This option will add new tournaments to Game Modes / Tournaments : UEFA CL, UEFA Europa League, World Cup, Confederations Cup, Copa America, Euro, etc. Be sure to not a start Career Mode while this option is selected or your game will get corrupted.